Skype is the quintessential video and voice chatting app--and you can use it on both Android and iOS. While the Android version of Skype does support video calling, it's not available on all devices.

Still, Skype is an excellent tool for making free or cheap phone calls--not only can you call from one Skype account to another for free, but you can make domestic and international calls at extremely low rates using your device's data plan or Wi-Fi connection.

Step 1: Install Skype

Skype is a free app for both Android and iOS devices. You can find the Skype iOS app in the App Store, while the Skype Android app is in the Android Market.

Supported iOS devices include: iPhone (3G, 3GS, and 4), iPod Touch (3rd and 4th generations), and iPad (1 and 2). Skype requires iOS 4.0 or later. If you have an iPod Touch 3rd generation or an iPhone 3G, you will be able to receive only video.

If you have an Android device, you may see two versions of Skype--one called "Skype for Android," and one called "Skype Mobile for Verizon."* If you have a Verizon Android device, you may download the Skype Mobile for Verizon app (otherwise, download the Skype for Android app). Skype Mobile for Verizon does not allow you to place domestic calls, but you can still place international calls over a 3G or Wi-Fi connection. Skype for Android, on the other hand, lets you place domestic and international calls over a 3G or Wi-Fi connection.

*For this article, I used Skype for Android, not the Verizon version. When I tested Skype for Android on a Droid X running Android 2.1, there was no video chat option.

Step 2: Set up Skype

Android: Once Skype for Android is installed, tap on the app to open it. You will be prompted to sign into your Skype account (or, if you don't have a Skype account, to sign up for one), using your Skype username and password.

You will then be prompted to sync your Skype contacts with your phonebook contacts. You can choose to sync all contacts, add phonebook contacts to your Skype list, or sync no contacts. If you add phonebook contacts to your Skype list, you'll be able to easily call your phonebook contacts directly from the Skype app.

Browsing contacts in Skype for Android.

On the main Skype screen, you'll see four buttons: Contacts, Recent, Call phones, and Profile. The "Recent" button shows recent events--for example, phone calls you've missed and instant messages your Skype contacts have sent you. The "Call phones" button takes you to a screen where you can call a physical phone (as opposed to a Skype username), and the "Profile" button lets you update your profile and status message.

The main screen in the Skype for Android app.

You can also access the Settings menu, where you can set up notifications, IM options, and whether Skype starts automatically when you turn on your phone.

iOS: Once Skype is installed, tap on the app to open it. You will be prompted to sign in using your Skype username and password. You must have a Skype account already created to use Skype on your iOS device--there is no option in the app to create a new account. You can create a new account for free by going to Skype's website.

Once you've signed in using your Skype login details, you will be taken directly to your contact list. Initially, you'll have only your previously saved Skype contacts in your contact list. To see contacts from your phone, tap the "Contacts" button in the top left corner. In the main Contacts menu you can find contacts from your iPhone, but you cannot import them to your Skype contact list.

The Contacts screen in the Skype iPhone app.

The iPhone version of Skype has four tabs: Contacts, Messages, Call, and My Info. The Messages tab lets you send instant messages to people on your Skype contact list, while the My Info tab lets you set up your profile, buy Skype credit, and set up voicemail.

Step 3: Make a Call

You can make two types of calls using Skype: Skype-to-Skype calls and Skype-to-Phone calls. The first, Skype-to-Skype calls, are free (though you may be charged if you are on a limited data plan), while the second, Skype-to-Phone calls, are billed at a low rate (for example, it's $0.019/minute--1.9 cents per minute--for calls to the United States).

To Make a Skype-to-Skype Call

Open up your Skype contact list. If you have an Android device, go to your Contacts list, tap the icon next to where it says "All contacts," and choose "Skype." If you have an iOS device, open up your Contacts list, tap the button in the upper left corner that says "Contacts," and, from the next screen, choose "Skype Contacts."

Then choose the Skype contact you want to call, and tap "Call." You also have the option to send them an instant message, or, if you're on an iOS device, to start a video call.

Calling Ron in Skype for iPhone.

To Make a Skype-to-Phone Call

If you want to call a regular phone line, tap the tab for Call phones (on Android) or Call (on iOS). If the person you want to call is saved in your phone's phonebook, you can tap the phonebook symbol (in the upper right corner on both Android and iOS) and choose a number from your phonebook. Otherwise, you can use the number pad to type in the phone number you want to call. Be sure to change the country code to the correct country (because Skype is an Internet calling service, there are no "domestic" calls).

You will be billed by Skype for all Skype-to-phone calls that you make using Skype's mobile apps. Calls are billed per minute.

Let's Skype!

As I noted earlier, Skype is the app everyone thinks of when they think of Internet calling. Skype is a great app for cheap data-connection or Wi-Fi calling, but it's not ideal if you want to make free Skype-to-Skype video calls.

For one thing, Skype video calling is available only on iOS devices (and on some devices--such as the iPod Touch 3rd generation and the iPhone 3G--you will only be able to receive video) and certain Android devices. Still, Skype is easy to use, nearly everyone seems to have it, and it's available on Windows, Mac, Linux, Android, iOS, Symbian, and a number of connected TVs. Plus, you can make cheap phone calls to real phone numbers--excellent if you routinely have to make international calls.

[Editor's Note: An earlier version of this article stated that Skype for Android did not support video calling. Skype for Android now does support video calling on 41 whitelisted devices.]

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